The present invention is directed toward improving the adhesion and adhesion retention between a rubber composition and metallic reinforcement cord, such as steel wire and cable which is embedded in the rubber stock. Flat sheets or strips of such stocks, reinforced with metal or fibers, are utilized as plies or other components in the manufacture of tires, repair stocks for retreading tires, conveyor belts, hoses and the like and are referred to in the art as rubber skim stocks. Skim refers to a relatively thin layer or coating of the rubber over the reinforcement filaments or cords. Greater thicknesses of rubber are also bonded to metal in other instances such as motor mounts and golf club shafts and these would not be termed skim stocks.
In the manufacture of the such rubber articles, particularly steel-belted bias and radial tires, reinforcing the rubber skim stock material with steel wire or cable is common. One of the more important uses for a metallic reinforced rubber is as a belt where one or more of these belts are substantially circumferentially oriented beneath the tread stock to maintain the integrity and shape of the tire during inflation and subsequent load. Other areas where metal reinforced rubber skim stock may be utilized is in the body ply, bead or chafer of a tire.
Many methods for promoting adhesion between vulcanizable rubber and steel reinforcement cords are known. For instance, steel reinforcement cords commonly are plated with compositions designed to promote and maintain adhesion to vulcanized rubber. This method generally promotes adhesion to vulcanized rubber wherever the surface plating contacts the vulcanized rubber. However, during construction of a tire, plated steel reinforcement cords are typically cut to fixed lengths, and the cutting process leaves a bright steel core exposed at the cross sections where cutting has occurred. As a result, the exposed bright steel core lacks the surface coating and therefore will not adhere to the vulcanized rubber of the tire, which could diminish tire performance. There is, therefore, a need for a method that promotes adhesion between a bright steel surface and vulcanized rubber.
To promote adhesion between rubber and ferrous metals it is known to employ a variety of metallic salts or complexes or other additives as coatings to the metal or as an ingredient in a rubber composition.
Thus, while others have sought to enhance adhesion between rubber compositions and bright steel by employing materials such as cobalt para-aminobenzoate and para-amino-benzoic acid in the stock, the art of which we are aware has not disclosed the exclusive use of the silane compounds set forth hereinbelow in a vulcanizable rubber stock to increase adhesion properties between rubber and metallic reinforcement, particularly bright steel.